The difference between these two men seems obvious: their faces are different, their hair is different—even their shirts are a different color. And yet an experiment by psychologists Dan Simons and Chris Chabris at Harvard reveals that our brains actually process very little of what comes in through the eyes. >> In this experiment, the subject comes up to a counter and a first experimenter hands them a consent form. As soon as they finish signing the consent form, they hand it back to the first experimenter, who then takes the consent form, ducks down behind the counter to put it away, and a different experimenter then stands up and hands the subject a packet of information and sends them into a hallway, where we ask them questions about it. >> This wonderful experiment uncovers an aspect of the brain's attention system known as "change blindness." >> Change blindness is the idea that we often miss large changes to our visual world from one view to the next. We're often not able to see large changes that would appear to be perfectly obvious to somebody who knows they're going to happen. >> And incredibly, in 75% of cases the subjects don't notice a thing. >> The lady who took me up here, she opened the door for me, and told me to walk over to the desk. >> Fill out this form. >> Alright. I think there was a sign that said "Experiment." >> Um-hmm. >> And a man there gave me a form to sign. >> Um-hmm. >> There was a guy standing under a big sign that said "Experiment." >> Um-hmm. >> And to my left there was, like, a pot with some dirt in it and some plastic containers. >> Is it the 5th? >> Ah, yes, it's the 5th. >> Oh, I filled out a form. >> Alright, this form. >> How long would it be about before it—and then I asked how long it would take, and he said about 10, 15 minutes or so. I guess I have the time to do that. >> Did you notice anything unusual at all after you signed the consent form? >> I just signed it, and I didn't even pay attention to anything that was written on it. >> Okay. Um, after, after you handed it back to him, did you notice anything unusual happen at all? >> If you can just take this into the next room. No, no I, I probably wasn't even looking that direction. >> Okay. >> I turned and looked towards the clear door and saw some people there. >> Okay. >> And then I turned back and looked at him for a second. >> Okay. Did you notice anything unusual at all after you signed the consent form? >> No. >> This is only going to take five or ten minutes? >> Yeah. >> Okay. >> It'll take, it'll be real short. >> Okay. >> The person who stood up was actually a different person. >> Okay. >> Um, I gather you didn't notice that that was different? >> No. >> A different person actually stood up and handed you this form, um, and sent you out toward me. Um, I gather from your reaction, you didn't notice that? >> No! >> Okay, um, don't, don't feel bad about that. Actually, most of the time, we find about 75% of people don't notice. >> You serious? >> Yeah. >> The person who stood up with the packet was actually a different person— >> Wow! >> than, ah, than the first person. >> That is incredible! >> So, I gather, I gather you didn't see it? >> I didn't catch that, no. >> Okay. >> What's really interesting is that some people notice these changes, and other people don't notice these changes. >> Okay. If you could just take this— >> And we really don't yet have a good idea what separates those people who don't from those people who do. It might be that there are individual differences, and some people are better able to detect these sorts of changes. But it's also possible that it's just coincidence, that the people who noticed it, just happened to be focusing on a feature that changed—they just happened to be paying attention to the color of the person's shirt— and the people who failed to notice it, just happened to be paying attention to something else.